1. Field of the Invention
The present invention relates to a water-cooled internal combustion engine in which coolant discharged from a coolant circulating pump is supplied to a block-side coolant jacket formed in a cylinder block via a head-side coolant jacket formed in a cylinder head.
2. Description of the Related Art
Conventionally, an internal combustion engine disclosed in JP-A-2000-282861 is known as an internal combustion engine of a water-cooled type. In this multi-cylinder internal combustion engine, a communicating path is provided at one end portion of a cylinder head in a direction in which cylinders are arranged therein, for guiding coolant discharged from a coolant circulating pump into a coolant jacket, and provided at the other end portion of the cylinder head in the cylinder arrangement direction are a thermostat, a by-pass passage and an outlet port through which coolant flowing out of a coolant jacket in a cylinder block is allowed to flow out into a radiator. Then, a heater core for air conditioning is disposed at an intermediate position between a hose connecting to a downstream portion of the coolant jacket in the cylinder head at a side of the cylinder head in a direction normal to the cylinder arrangement direction and a hose connecting to a downstream portion of a coolant passage formed in the cylinder block. In addition, formed integrally in a thermostat cover which covers the thermostat are an inlet opening to which a radiator hose through which coolant from a radiator flows is connected and an outlet opening to which a radiator hose through which coolant returning to the radiator flows is connected.
On the other hand, a relatively large amount of exhaust gases is returned to an intake system of the internal combustion engine, or an excessive amount of air is supplied to the intake system for lean burning as part of a combustibility improving technology for, for example, improving the combustibility of the internal combustion engine by generating eddy currents in combustion chambers thereof. In such a lean-burn internal combustion engine or an internal combustion engine of a small displacement, there is generated less heat from combustion, and the temperature of coolant for cooling the cylinder head and the cylinder block is not increased to a temperature level which is sufficient to match the heating performance required for an air conditioner designed to employ heat transferred by the coolant.
Then, in order to improve the heater performance, there have been proposed various technologies for increasing the temperature of coolant supplied to the heater core of the air conditioner among which is the provision of an auxiliary heating device along a coolant passage which communicates with the heater core. In an internal combustion engine, however, such as one disclosed in the aforesaid unexamined patent publication, the coolant hose for supplying coolant to the heater core is just connected to the downstream portion of the coolant jacket of the cylinder head and no consideration is taken into for increasing the temperature of the coolant which is supplied to the heater core.
In addition, the coolant hose which connects to the heater core is connected to the cylinder head on a different side of the cylinder head from the side at the other end of the cylinder head where the thermostat cover is mounted, and therefore, this results in the fact that the coolant outlet ports are situated at scattering locations on the cylinder head, leading to a difficulty in performing hose connecting work efficiently. Thus, there has been a demand for improving the situation from the viewpoint of efficient assembly of internal combustion engines.
The present invention was made in view of the situation, and a common object of first to third aspect of the invention is to improve the heater performance of a water-cooled internal combustion engine in which coolant discharged from a coolant circulating pump is supplied to a block-side coolant jacket formed in a cylinder block via a head-side coolant jacket formed in a cylinder head by increasing the temperature of coolant supplied to a heater core with a simple construction by devising the location of an inlet port formed in the head-side coolant jacket for coolant from the coolant circulating pump and an outlet port for coolant supplied to the heater core. Furthermore, an object of the second aspect of the invention is to have a compact internal combustion engine by providing a compact routing for coolant passage forming members such as hoses connecting to the radiator and the heater core at a portion where an outlet portion for supplying coolant to the heater core is provided. Moreover, an object of the third aspect of the invention is to improve the assembling performance of an internal combustion engine, as well as to reduce the number of components involved by improving the efficiency of connecting work of coolant passage forming member such as hoses connected to the radiator and the heater core.
With a view to achieving the objects, according to the first aspect of the invention, there is provided a water-cooled internal combustion engine with cylinders and a crankshaft in which coolant discharged from a coolant circulating pump is supplied to a block-side coolant jacket formed in a cylinder block via a head-side coolant jacket formed in a cylinder head, the water-cooled internal combustion engine being characterized in that an inlet port through which the coolant discharged from the coolant circulating pump is allowed to flow into the head-side coolant jacket is provided at one end portion in a cylinder-head center line direction and an intake side of the cylinder head, and in that a first outlet port through which the coolant from the head-side coolant jacket is allowed to flow out into a heater core is provided at the other end portion in the cylinder-head center line direction and an exhaust side of the cylinder head.
According to the construction of the first aspect of the invention, since the inlet port is situated at the one end portion in the cylinder-head center line direction and the intake side of the cylinder head and the first outlet port is situated at the other end in the cylinder-head center line direction and the exhaust side of the cylinder head, respectively, the distance between the inlet port and the first outlet port can be made longer within a coolant jacket forming range, whereby the amount of heat that the coolant can receive is increased, thereby making it possible to increase the temperature of the coolant that is supplied to the heater core, resulting in the improvement of the heater performance. Moreover, since the construction for increasing the temperature of the coolant supplied to the heater core depends on the location of the inlet port and the outlet port in the cylinder head, the construction can be made simple. In addition, since the inlet port is situated on the intake side of the cylinder head, intake ports formed in the cylinder head are cooled with coolant whose temperature is lower when compared with a case where the inlet port is made to open on the exhaust side of the cylinder head, whereby the loading efficiency can be improved.
According to the second aspect of the invention, there is provided a water-cooled internal combustion engine as set forth in the first aspect of the invention, wherein an accommodating chamber for accommodating therein a thermostat is provided at the other end portion and an intake side of the cylinder head.
According to the construction of the second aspect of the invention, in addition to the advantage provided by the first aspect, the following advantage is provided. Namely, since the accommodating chamber for accommodating the thermostat is provided at the other end and on the intake side of the cylinder head where a space is formed compared with the exhaust side of the cylinder head where the coolant passage forming members such as the hose for connecting the heater core and the first outlet port are provided, the coolant passage forming members including the coolant passage forming member such as the hose for connecting the thermostat to the radiator can be disposed compact at the other end portion of the cylinder head in the cylinder-head center line direction, thereby making it possible to have the compact internal combustion engine.
According to the third aspect of the invention, there is provided a water-cooled internal combustion engine as set forth in the second aspect of the invention, wherein a thermostat cover for covering the thermostat is provided on a mount surface formed on the other end portion, wherein the accommodating chamber, the first outlet port, and a second outlet port through which the coolant from a main body of the internal combustion engine is allowed to flow out into a radiator are made to open in the mount surface, the accommodating chamber being situated on an intake side and the first outlet port and the second outlet port being situated on an exhaust side of the mount surface, and wherein an inlet passage through which coolant from the radiator is allowed to flow into the thermostat, a first outlet passage through which coolant from the first inlet port is allowed to flow out into the heater core and a second outlet passage through which coolant from the second outlet port is allowed to flow out into the radiator are formed in the thermostat cover.
According to the construction of the third aspect of the invention, in addition to the advantage provided by the second aspect of the invention, the following advantage is provided. Namely, on the mount surface at the other end portion of the cylinder head where the thermostat cover is mounted, the inlet passage, the first outlet passage and the second outlet passage which communicate with the accommodating chamber provided on the mount surface, the first outlet port and the second outlet port, respectively, are formed in the thermostat cover which is single member, and moreover, the inlet passage, the first outlet passage and the second outlet passage are disposed collectively at the other end portion of the cylinder head. Thus, the construction facilitates the connection of the inlet passage, the first outlet passage and the second outlet passage to the coolant passage forming members for connecting those passages to the radiator, the heater core and the radiator, respectively, whereby the efficiency of the connecting work can be improved to thereby improve the assembling efficiency of the internal combustion engine. In addition, the construction obviates the necessity of separately preparing members required to supply the coolant to the heater core such as joints, which reduces the number of components involved, as a result of which man hours associated with the assembly of the joints can be reduced, this contributing to the improvement in the assembling performance of the internal combustion engine.
Note that as used herein, the term xe2x80x9cviewed from the topxe2x80x9d means viewing from a centrally axial direction of a cylinder bore, and the terms xe2x80x9cintake-valve-port side port wall portionxe2x80x9d and xe2x80x9cexhaust-valve-port side port wall portionxe2x80x9d mean, respectively, an intake-port wall and an exhaust-port wall which are included within the range of the cylinder bore as viewed from the top. In addition, the term xe2x80x9ccylinder-head center linexe2x80x9d means a straight line in the cylinder head when viewing from the centrally axial direction of the cylinder, an imaginary plane including central axes of the cylinder bores and the rotational axis of the crankshaft or an imaginary plane including the central axes of the cylinder bores and being parallel to the rotational axis of the crankshaft. Additionally, the terms xe2x80x9cintake sidexe2x80x9d and xe2x80x9cexhaust sidexe2x80x9d mean, respectively, a side of the cylinder head where inlet ports for the intake ports are situated and the other side of the cylinder where outlet ports for the exhaust ports are situated, relative to the imaginary planes.